1. Field of the Invention
The present invention relates to manufacturing a semiconductor device, and more particularly, to a method of electron beam lithography for minimizing throughput loss and preventing butting errors from occurring.
A claim of priority is made to Korean Patent Application No. 2002-0047230, filed Aug. 9, 2002, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Among semiconductor fabricating processes, a lithography process using an electron beam is used to transfer a delicate pattern. Until now, lithography using a electron beam has generally been used for fabricating a photo mask in which printing a delicate pattern is regarded as a very important factor.
When a mask is fabricated using the electron beam, the size of the electron beam is limited to a very small region, and so it is difficult to expose the whole mask. Therefore, electron beam lithography equipment will divide the region to be exposed to light into several segments, divide each of the segments into several stripes or frames, and then expose sequentially each of the stripes to the electron beam.
Since an optical system for the electron beam employed in the electron beam lithography equipment is limited in comparison to a typical optical system, it is necessary to divide the region to be exposed into several segments and to divide each of the segments into several stripes, in order to expose each of the stripes to the electron beam. In electron beam lithography, a chip region to be exposed is divided into regions having a certain length.
Electron beam lithography equipment, such as equipment of the MEBES family of ETEC, Inc. (located in the U.S.A), typically is configured to expose stripes of about 1 mm in width each. Electron beam lithography equipment of Toshiba, Inc. (located in Japan) is configured to expose frames. However, this equipment is similar in that they divide the region to be exposed into certain small units such as stripes or frames.
When the stripes or frames are sequentially exposed to the electron beam, a so-called butting error, i.e. wrenching between adjacent stripes, occurs. The butting error represents an error in which a pattern ranging over an interval between the stripes, which is transferred by the exposure, is wrenched or dropped from the stripe boundary. Because of the butting error, a critical dimension error in which the critical dimension of the pattern in the stripe boundary changes, or a position error in which a pattern position is wrenched may occur.
The butting error is sometimes called a stitching error in a method for scanning the electron beam, e.g., a vector scan or a raster scan. However, most butting errors are due to wrenching of the stripes when the stripes are scanned by the electron beam. In order to overcome such butting errors, a multi-pass printing method has been developed.
FIG. 1 a schematic diagram of a method for sequentially exposing the electron beam to each of the stripes. FIG. 2 is a schematic diagram of a typical multi-pass printing method.
Referring to FIG. 1, a region to be exposed is divided into several segments and each of the segments into N stripes, and then each of the stripes are sequentially exposed. For example, a first stripe is exposed, and then other stripes are sequentially exposed. When the exposure of an Nth stripe has been completed, the exposure of an entire segment is completed.
However, the multi-pass printing method includes performing several exposure passes, as shown in FIG. 2, so as to prevent butting errors which may be caused when exposure is sequentially performed for each of the stripes. Performing several exposure passes includes setting an offset from the first stripe position, or in other words moving a stripe. For example, the process involves moving a stripe of a second exposure pass by a half or a quarter of the width of a stripe used in a first exposure pass, performing the second exposure pass, and repeating the above steps. Here, when two exposure passes constitute the whole exposure process, the amount of each exposure pass may be half of a target dose.
As a result, exposure inferiority at a boundary between stripes, which results during the first exposure pass, may be compensated for to a certain degree during the second exposure pass (or a third or a fourth exposure pass). As a result, butting errors can be effectively prevented. In practice, butting errors decrease in proportion to the number of the exposure passes.
However, when electron beam lithography is performed using the multi-pass printing method, the time between exposure passes increases in proportion to the number of exposure passes. Accordingly, the time necessary for electron beam lithography increases, a fact which ultimately causes a throughput loss.